Modbus
- Thread starter Pardep
- Start date
Can you explain a little more detail.
Modbus Master will request data from slave! Is this Modbus Rtu or Tcp?
Rtu will probably have to have "Terminating Resister" at ENDPOINTS!
Slave will have to have unique ID.
Some type of serial protocol such as Baud Rate, Stop Bit, Parity, (Same on all devices - except ID.)
Tcp is modbus over ethenet so a unique IP address.
In case of using Modbus RTU or ASCII (serial) it would also be good to tell us the type and length of communication cable, and if the cable is installed on a separate path or next to power cables, and if you are using RS-232, RS-422 or RS-485 ...
bernie_carlton
Lifetime Supporting Member + Moderator
I would guess that the Modbus request is being generated too quickly with each possibly communicating over the reply from the previous request. Make sure to utilize whatever indication of a completed request is available in your system before beginning the next.
- As bernie_carlton said any request must wait until the previous one has got the answer.
- The cable must be a specific one for RS-485, a normal cable that is not twisted or shielded will not work and even more if it passes close to power wiring.
- The terminating resistors must be installed on both ends
- Both Comm ports must be configured with 8 data bits, never with 7 data bits. This is necessary due Modbus RTU transmits the pure binary value, not the ASCII representation.
- Don't try to use a very high baud rate, if with 38400 bauds you have problems then try with 19200, if still problems try 9600 ... 4800 etc.
- The cable must be a specific one for RS-485, a normal cable that is not twisted or shielded will not work and even more if it passes close to power wiring.
- The terminating resistors must be installed on both ends
- Both Comm ports must be configured with 8 data bits, never with 7 data bits. This is necessary due Modbus RTU transmits the pure binary value, not the ASCII representation.
- Don't try to use a very high baud rate, if with 38400 bauds you have problems then try with 19200, if still problems try 9600 ... 4800 etc.
danw
Lifetime Supporting Member
what does the protocol 132 error mean?
Have you tried setting the master poll rate at something slow, like once every 15 seconds, to see if the slave can respond for every poll?
Have you tried setting the master poll rate at something slow, like once every 15 seconds, to see if the slave can respond for every poll?
132 is...Signals that a fieldbus data transfer timed out. This can occur if the slave device does not reply in time or does not reply at all. A wrong unit address will also cause this error. On some occasions, this exception is also produced if the characters received don't constitute a complete frame.
ya i tried many time stamps......
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